MYC is a transcription factor that targets a large fraction (~15%) of the genome and is tightly regulated in normal cells and essential for normal development and homeostasis in most animals. Deregulated MYC expression (e.g., overexpression) is tumorigenic in mice and associated with most types of cancer in humans. MYC deregulation may occur via alterations of the c-myc gene itself (e.g., translocation and amplification) or via aberrant activation of upstream signaling pathways that activate c-myc gene expression and/or increase MYC protein stability via post-translational modifications (PTMs). The PTMs of MYC are, however, poorly characterized and their roles in the multiple cellular and molecular activities of MYC are still poorly defined and controversial. Until recently phosphorylation and O-glycosylation of a few residues were the only PTMs reported, which affect MYC ubiqitination and degradation by the proteasome. Our lab recently uncovered novel PTMs of MYC and found that MYC is acetylated at several lysine (K) residues by transcription coactivators with histone acetyltransferase (HAT) activity (i.e., GCN5 and p300). The general objective of my research is to provide definitive evidence that native MYC in mammalian cells is regulated via acetylation and to define the cellular and molecular functions of MYC acetylation at specific residues. AIM 1: To establish and characterize acetylation of native MYC in mammalian cells using acetylated site-specific antibodies (MYC-K148Ac, MYC-K157Ac, MYC-K323Ac) Acetylation of endogenous MYC has yet to be demonstrated in any cell type. I will use new antibodies that recognize specifically human MYC acetylated residues K148, K157, and K323 to profile acetylation of MYC at these different sites in several non-transformed and transformed/cancer cell lines. AIM 2: To identify functions of MYC acetylated residues K148(149) and K157(158) I will test the role of MYC acetylated residues K148 and K157 (human coordinates homologous to mouse MYC K149 and K158) in MYC-induced cell proliferation, transformation and apoptosis. AIM 3: To establish and define the role(s) of MYC acetylation in target gene regulation Selected MYC target genes affected by the R158 (or R149) substitution identified in preliminary experiments (e.g. Nrf1) and in Aim 2 will be analyzed to tes the possible role of acetylation at K158 (or K149) in regulating MYC transcription functions. Various methods, including chromatin immunoprecipitation (ChIP) assays, RNA interference (RNAi), and reporter gene assays will be used.